A conventional mini dim light has a lamp holder that may be rotated and thereby adjusted to different angular positions relative to a wall receptacle. To this effect, two pins on the mini dim light for plugged in pin slots on the wall receptacle are connected to two concentric annular conductive plates having different diameters, and two conductive leaf springs in the lamp holder have extended length and two projected portion formed on two tree ends thereof, such that the projected portions may separately slide on the two concentric annular plates. When the projected portions on the free ends of the conductive leaf springs are slid into two recesses on the concentric annular plates, the lamp holder is stably electrically connected to the pins.
In the above structure to enable a rotatable lamp holder, since the concentric annular plates occupy a considerable volume, the structure is only suitable for a mini dim light without being used in other types of lighting fixtures. Moreover, since the leaf springs of the lamp holder slid over the annular plates must engage with the recesses on the annular plates to enable electric connection of the leaf springs to the pins, this type of rotatable mini dim light is stably made only at some particular angular positions. In other words, such conventional mini dim light is not workable at all angular positions. Instead, it is only workable in some specific directions.
There might be two or three pin slots on each socket on a wall receptacle. Power may be output from an external power source to an electrical appliance or a receptacle connected to an extension cord only when a plug connected to the appliance or the receptacle having at least two conductive pins is plugged in the socket on the wall receptacle. Once the plug is plugged in the socket, the at least two pins together fix the plug to a fixed direction, making the whole plug non-rotatable relative to the wall receptacle. As a result, a power cord extended behind the plug tends to become twisted or exert a pull force to damage the plug.
There are simple electric appliances, such as a mini dim light, which do not have a power cord connected thereto or a rotatable structure. When such an electric appliance is plugged in a wall receptacle that has pin slots arranged in an undesired direction, the appliance would be connected to the wall receptacle in a lying or an inverted position to cause inconvenience in use.